Applications exist where it may be necessary to penetrate a sealed container with one or more electrical leads or electrical contacts so as to provide electrical access to and from electrical components enclosed therein. One such application may be for an electrochemical cell or for an implantable medical device. Such an implantable medical device may comprise for example, an implantable drug pump, an implantable sensor capsule, a cochlear implant, an implantable pulse generator (IPG) such as those adapted for providing deep brain stimulation, nerve stimulation, electrical pacing therapy and cardiac rhythm management techniques (e.g., for delivering electrical stimulation therapy for various cardiac arrhythmias). In addition, such implantable electronic devices can be used to sense optical signals or deliver optical impulses for stimulation. All such devices, including discrete electrochemical cells, are intended to be covered under the rubric of implantable medical devices.
A typical implantable medical device can have one or more housing or encasement members for isolating the active contents of an electrochemical cell (e.g., battery or capacitor) which can be coupled to one or more electrical components within and/or coupled to the implantable medical device. The implantable medical device typically has at least two major outer housing members that form a hermetically-sealed housing when welded together to provide a hermetically-sealed interior space for the components of the implantable medical device.
Electrical feedthrough assemblies are provided to form a conductive path extending between the interior of the hermetically-sealed housing and the exterior of the housing. The conductive path comprises a conductive pin or terminal that is electrically insulated from the housing. Many feedthrough assemblies, which are known in the art, include the terminal, a ferrule surrounding the terminal, an insulating body such as a glass or ceramic (including alumina) material for positioning and insulating the pin within the ferrule, and an epoxy backfill of the ferrule, over the insulator and around the terminal.
Feedthrough corrosion may be encountered when the feedthrough assembly components come into contact with body fluids or electrolytes, if fluid leak paths form in the backfill or at the interface of the backfill with the terminal and or ferrule. In addition, defects in components of the feedthrough assembly, such as the insulating body, have been observed to result in corrosion.
Conventionally, visual inspection has been used to identify the presence of defects in the feedthrough assembly components. The visual inspection is qualitative and inherently prone to operator error and variation. What is needed is a performance measurement to enable a quantitative electrical isolation assessment.